A MIMO (Multi-input Multi-output) antenna technology is a core technology in MIMO wireless communications technologies. A conventional SISO (Single-input Single-output) antenna system has an unbreakable bottleneck in a channel capacity-limitation of a Shannon capacity. When no size is limited, a throughput rate of a system is multiplied with an increasing quantity of antennas.
However, a size of a terminal device is strictly limited. When multiple antennas are concentrated in small space, great mutual coupling may be caused, and performance of the antennas deteriorates accordingly. How to implement high isolation between multiple antenna units on a terminal side in a case of a limited size is a difficulty in antenna design.
In an existing method for implementing high MIMO antenna isolation, two antenna units are connected by using a neutralization line, and a coupling current between the antennas is neutralized by using the neutralization line, and therefore antenna isolation is improved. However, in this manner in which the neutralization line is used, only an antenna that operates in a specific frequency band can be isolated. If an operating frequency of the antenna changes, neutralization lines of different lengths are required.